Sesquiterpenes from the Fungus Antrodiella albocinnamomea with Cytotoxicity and Antibacterial Activity

Eight new sesquiterpenes, namely, albocinnamins A−H (1−8), along with two known ones (9 and 10), have been isolated from the fungus Antrodiella albocinnamomea. Compound 1 possesses a new backbone that might be derived from cadinane-type sesquiterpene. Structures of the new compounds were elucidated by detailed spectroscopic data analysis, single-crystal X-ray diffraction, and ECD calculations. Compounds 1a and 1b showed cytotoxicity against SW480 and MCF-7 cells, with IC50 values ranging from 19.3 to 33.3 μM, while compound 2 displayed cytotoxicity against the HL-60 cell with an IC50 value of 12.3 μM. In addition, compounds 5 and 6 exhibited antibacterial activity against Staphylococcus aureus with MIC values of 64 and 64 µg/mL, respectively.


Introduction
Antrodiella albocinnamomea is a white-rot basidiomycetous fungus belonging to Basidiomycota, which is widely distributed in temperate to subtropical areas of China [1]. Previous studies show that A. albocinnamomea is highly productive for bioactive sesquiterpenes, including cadinane, triquinane, chamigrane, humulane, and gymonmitrane classes [2][3][4][5][6][7][8]. Representative sesquiterpenes are antroalbocin A, antroxazole A, antrodillin, and antroalbol H. Antroalbocin A is a novel bridged tricyclic sesquiterpene with antibacterial activity against Staphylococcus aureus [9]. Antroxazole A is an interesting chamigrane dimer containing an oxazole moiety, showing selective inhibition on LPS-induced B lymphocyte cell proliferation [10]. Antrodillin is a triquinane sesquiterpene derivative that also showed immunosuppressive activity [11]. Antroalbol H is a chamigrane sesquiterpene that has potential anti-diabetic activity [12]. Such rich sesquiterpene resources prompted us to carry out further research on this fungus. As part of our long-term research into the chemical composition of fungi, we conducted the secondary metabolites on the cultural broth of the fungus A. albocinnamomea in rice medium. Herein, the isolation, structural elucidation, and antibacterial activity of these isolates (Figure 1) are reported.

General Expriment Procedures
Melting points were measured on an X-4 micro melting point apparatus. Optical rotations were acquired using a Rudolph Autopol IV polarimeter. UV and CD spectra were recorded on a UH5300 UV-VIS Double Beam Spectrophotometer and an Applied Photophysics Chirascan-Plus spectrometer. IR spectra were conducted on a Shimadzu Fourier transform infrared spectrometer with KBr pellets. 1D and 2D NMR spectra were recorded on a Bruker Advance III 600 spectrometer using TMS as a ternal standard. Chemical shifts (δ) are reported in parts per million (ppm). HRESIMS data were obtained on a Thermo Scientific Q Exactive Orbitrap MS system. X-ray crystallographic analysis was conducted on the BRUKER D8 QUEST. Colum chromatography (CC) was carried out using silica gel (200-300 and 500-800 mesh, Qingdao Marine Chemical Ltd., Qingdao, China), RP-18 gel (20-45 µ , Fuji Silysia Chemical Ltd., Aichi, Japan), and Sephadex LH-20 (Pharmacia Fine Chemical Co., Ltd., Uppsala, Sweden). Medium Pressure Liquid Chromatography (MPLC) was performed on Biotage SP1 equipment, and columns were packed with RP-18 gel. High performance liquid chromatography (HPLC) was performed on Agilent 1260 system, equipped with DAD detector, Agilent ZORBAX SB-C18 column (5 µ m, 4.6 × 150 mm) and Agilent XDB-C18 column (5 µ m, 9.4 × 150 mm or 21.2 × 150 mm). The results were monitored by thin-layer chromatography (TLC). All solvents used were of analytical grade.

Fungal Material
The fungus A. albocinnamomea was collected from rotting poplar trees in Changbai Mountain Nature Reserve, Jilin Province of China, on 20 October 2009. It was identified by Professor Yu-Cheng Dai (Beijing Forestry University). The fungal specimen (CGBWSHF00182-4) has been deposited at the School of Pharmaceutical Sciences, South-Central Minzu University, China. The strain was cultured on plates of potato dextrose agar (PDA) medium at 25 °C for 6 days. After that, several pieces of mycelium were inoculated into rice culture medium (100 g of rice, 100 mL of water, in each 500 mL culture bottle). A total of 200 bottles were incubated fixedly at 25 °C for 40 days in a dark place.

Extraction and Isoation
The fermented material was extracted five times with absolute methanol. The extract was dissolved in water and EtOAc, and extracted four times with EtOAc to yield 124.0 g. As shown in Scheme 1, the crude extract was separated into 9 fractions (A−I) using a CC over silica gel column (80-100 mesh) with a solvent system of CH2Cl2−MeOH (from 100:0

General Expriment Procedures
Melting points were measured on an X-4 micro melting point apparatus. Optical rotations were acquired using a Rudolph Autopol IV polarimeter. UV and CD spectra were recorded on a UH5300 UV-VIS Double Beam Spectrophotometer and an Applied Photophysics Chirascan-Plus spectrometer. IR spectra were conducted on a Shimadzu Fourier transform infrared spectrometer with KBr pellets. 1D and 2D NMR spectra were recorded on a Bruker Advance III 600 spectrometer using TMS as a ternal standard. Chemical shifts (δ) are reported in parts per million (ppm). HRESIMS data were obtained on a Thermo Scientific Q Exactive Orbitrap MS system. X-ray crystallographic analysis was conducted on the BRUKER D8 QUEST. Colum chromatography (CC) was carried out using silica gel (200-300 and 500-800 mesh, Qingdao Marine Chemical Ltd., Qingdao, China), RP-18 gel (20-45 µ, Fuji Silysia Chemical Ltd., Aichi, Japan), and Sephadex LH-20 (Pharmacia Fine Chemical Co., Ltd., Uppsala, Sweden). Medium Pressure Liquid Chromatography (MPLC) was performed on Biotage SP1 equipment, and columns were packed with RP-18 gel. High performance liquid chromatography (HPLC) was performed on Agilent 1260 system, equipped with DAD detector, Agilent ZORBAX SB-C18 column (5 µm, 4.6 × 150 mm) and Agilent XDB-C18 column (5 µm, 9.4 × 150 mm or 21.2 × 150 mm). The results were monitored by thin-layer chromatography (TLC). All solvents used were of analytical grade.

Fungal Material
The fungus A. albocinnamomea was collected from rotting poplar trees in Changbai Mountain Nature Reserve, Jilin Province of China, on 20 October 2009. It was identified by Professor Yu-Cheng Dai (Beijing Forestry University). The fungal specimen (CGBWSHF00182-4) has been deposited at the School of Pharmaceutical Sciences, South-Central Minzu University, China. The strain was cultured on plates of potato dextrose agar (PDA) medium at 25 • C for 6 days. After that, several pieces of mycelium were inoculated into rice culture medium (100 g of rice, 100 mL of water, in each 500 mL culture bottle). A total of 200 bottles were incubated fixedly at 25 • C for 40 days in a dark place.

ECD Calculations
The Gaussian 16 program package was used for the calculations of the ECD spectra of 1−3, 6−7. The stable conformers subjected to ECD calculation were optimized using the timedependent density functional theory (TDDFT) method at the B3LYP/6-311G (d, p) level of theory [13,14]. The ECD curves were extracted by SpecDis 1.60 and weighted by Boltzmann distribution after UV correction [15]. For details, see the Supporting Information below.

X-Ray Crystallographic Analysis
Single crystals of compounds 1(1a/1b) and 5 were obtained from MeOH and H 2 O, and all single crystals were collected by a Bruker D8 QUEST diffractometer, which was equipped with Cu-Kα radiation (λ 1.54178 Å). The structure was solved with ShelXT, using direct methods and refined with ShelXT using least square minimization. Crystallographic data for compounds 1 and 5 have been deposited at the Cambridge Crystallographic Data Centre (CCDC number for 1: 2253029, and 5: 2253030).

Antibacterial Assay
All compounds were subjected to minimal inhibitory concentration (MIC) tests against two species of bacteria (S. aureus and Mycobacterium tuberculosis). Both bacteria were purchased from China General Microbiological Culture Collection Center (CGMCC). All strains were cultured in Mueller Hinton broth (MHB) (Guangdong Huankai Microbial Sci. &Tech. Co., Ltd., Guangzhou, China) at 37 • C. A sample of each culture was then diluted 40-fold in fresh MHB broth and incubated at 37 • C with shaking (200 rpm) for 2.5 h [16]. The resultant mid-log phase cultures were diluted to a concentration of 5 × 10 5 CFU/mL, and then 50 mL was added to each well of the compound-containing plates, giving a final compound concentration range of 128 or 50 mg/mL. The plates were observed after 24 h incubation at 37 • C [17]. Inhibition rates were determined using photometry at OD 625 nm . Rifampicin was used as the positive control (MIC < 2.5 µg/mL).

Cytotoxicity Assay
All compounds were assessed for their cytotoxicity toward the human promyelocytic leukemia (HL-60), colon cancer (SW480), and breast cancer (MCF-7) cell lines. All the cells were seeded into 96-well plates containing DMEM or RPMI1640 medium with 10% FBS under a 5% CO 2 atmosphere at 37 • C. The assays were performed by the MTS method according to the manufacturer's instructions [18]. Briefly, the isolated compounds dissolved in dimethyl sulfoxide (DMSO) and were then diluted with culture media to produce difference concentrations (40, 20, 10, 5, 2.5, 1.25, 0.625 µM). After incubation for 24 h, various levels of compounds were added to each well and incubated for 48 h. A total of 100 µL of culture media and 20 µL of MTS solution were added, which incubated for 3 h at 37 • C [19]. The absorbance of each well was measured at 490 nm using the Multi-Mode microplate reader. Paclitaxel was used as a positive control, and the concentrations for paclitaxel were 0.5, 0.25, 0.125, 0.0625, 0.03125, 0.015625, and 0.0078125 µM (IC 50 < 0.08 µM).

Results and Discussion
Compound 1 was isolated as colorless crystals. Its molecular formula was determined as C 15 (Table 1) showed 15 carbon signals, including four CH 3 , five CH, and six non-protonated carbons. Primary analysis of these data indicated that 1 had a benzene group and two carbonyl carbons. The 1 H-1 H COSY data revealed three fragments, as shown in Figure 2. Based on this, the HMBC data revealed the planar structure of 1 (Figure 2). At first, the HMBC correlations from H 3 -14 to C-1 and from H-11 to C-3, C-4, C-5 indicated one methyl group placed at C-1 and an isopropyl group placed at C-4 of the benzene group, respectively. In addition, the HMBC correlations from H-6 to C-9 (δ C 173.3) suggested a γ-lactone fused with the benzene group. Finally, the HMBC correlations from H 3 -15, H-6 and H-7 to C-8 (δ C 176.9) suggested a carboxyl group of C-8, in connection with C-7. Hence, the planar structure of 1 was established as an aromatic sesquiterpene with a novel backbone. A single crystal X-ray diffraction experiment was performed (Figure 3), and the result confirmed the planar structure as given above. In addition, the data revealed the relative configuration of 1 and suggested that 1 should be a racemate. Therefore, compound 1 was separated into two pure enantiomers by chiral-phase HPLC ( Figure S22), and the absolute configurations were determined by comparing the calculated and experimental ECD spectra (1a/1b, Figure 4). This experiment enabled 1a and 1b to be determined as (+)-(6S,7R) and (−)-(6R,7S), respectively. Consequently, the structure of 1 was characterized and trivially named as (±)-albocinnamin A.
photometry at OD625 nm. Rifampicin was used as the positive control (MIC < 2.5 µ g/mL).

Cytotoxicity Assay
All compounds were assessed for their cytotoxicity toward the human promyelocytic leukemia (HL-60), colon cancer (SW480), and breast cancer (MCF-7) cell lines. All the cells were seeded into 96-well plates containing DMEM or RPMI1640 medium with 10% FBS under a 5% CO2 atmosphere at 37 °C . The assays were performed by the MTS method according to the manufacturer's instructions [18]. Briefly, the isolated compounds dissolved in dimethyl sulfoxide (DMSO) and were then diluted with culture media to produce difference concentrations (40, 20, 10, 5, 2.5, 1.25, 0.625 µ M). After incubation for 24 h, various levels of compounds were added to each well and incubated for 48 h. A total of 100 µ L of culture media and 20 µ L of MTS solution were added, which incubated for 3 h at 37 °C [19]. The absorbance of each well was measured at 490 nm using the Multi-Mode microplate reader. Paclitaxel was used as a positive control, and the concentrations for paclitaxel were 0.5, 0.25, 0.125, 0.0625, 0.03125, 0.015625, and 0.0078125 µ M (IC50 < 0.08 µ M).

Results and Discussion
Compound 1 was isolated as colorless crystals. Its molecular formula was determined as C15H19O3 by HRESIMS (measured at m/z 263.12769 [M + H] + ; calcd for C15H20O3, 263.12779), which accounted for seven double-bond equivalents. The 1 H NMR and 13 C NMR spectrum (Table 1) showed 15 carbon signals, including four CH3, five CH, and six non-protonated carbons. Primary analysis of these data indicated that 1 had a benzene group and two carbonyl carbons. The 1 H-1 H COSY data revealed three fragments, as shown in Figure 2. Based on this, the HMBC data revealed the planar structure of 1 ( Figure  2). At first, the HMBC correlations from H3-14 to C-1 and from H-11 to C-3, C-4, C-5 indicated one methyl group placed at C-1 and an isopropyl group placed at C-4 of the benzene group, respectively. In addition, the HMBC correlations from H-6 to C-9 (δC 173.3) suggested a γ-lactone fused with the benzene group. Finally, the HMBC correlations from H3-15, H-6 and H-7 to C-8 (δC 176.9) suggested a carboxyl group of C-8, in connection with C-7. Hence, the planar structure of 1 was established as an aromatic sesquiterpene with a novel backbone. A single crystal X-ray diffraction experiment was performed (Figure 3), and the result confirmed the planar structure as given above. In addition, the data revealed the relative configuration of 1 and suggested that 1 should be a racemate. Therefore, compound 1 was separated into two pure enantiomers by chiral-phase HPLC ( Figure  S22), and the absolute configurations were determined by comparing the calculated and experimental ECD spectra (1a/1b, Figure 4). This experiment enabled 1a and 1b to be determined as (+)-(6S,7R) and (−)-(6R,7S), respectively. Consequently, the structure of 1 was characterized and trivially named as (±)-albocinnamin A.     Compound 2 was isolated as a colorless oil. Its molecular formula was determined as C15H22O2 by HRESIMS (measured at m/z 235.16927 [M + H] + ; calcd for C15H23O2 235.16926), which accounted for five degrees of unsaturation. The 1 H and 13 C NMR data ( Table 1) Figure 2, which established the OH position at C-3 and revealed the α,β-unsaturated keto moiety to be 6,7-en-8-one. Based on this, the HMBC correlations from H-14 to C-1, C-2, and C-10 constructed a six-membered ring. In addition, the HMBC correlations from H-9 to C-8 and C-7 established another six-membered ring. Therefore, compound 2 was assigned as a bicyclic cadinane sesquiterpene [20]. In the ROESY spectrum ( Figure 5), observed cross peaks of H-3/H-5, H-12 and H-5/H-10 indicated that H-3, H-5 and H-10 were in the same orientation, and H-4 was in the other orientation. There, correlations revealed the relative configuration of 2 (3S,4R,5S,6R or 3R,4S,5R,6S). Finally, the absolute configurations were determined by comparing the calculated and experimental ECD spectra (Figure 4). Hence, the structure of 2 was identified and trivially named as albocinnamin B. Compound 2 was isolated as a colorless oil. Its molecular formula was determined as C 15 3 , one CH 2 , seven CH, and three non-protonated carbons. Of them, data at δ C 152.1 (d, C-6), 135.1 (s, C-7) and 201.0 (s, C-8) indicated the presence of an α,β-unsaturated keto moiety, while one signal at δ C 69.3 (d, C-3) suggested one OH group. The 1 H-1 H COSY correlations disclosed a long link, as shown in Figure 2, which established the OH position at C-3 and revealed the α,β-unsaturated keto moiety to be 6,7-en-8-one. Based on this, the HMBC correlations from H-14 to C-1, C-2, and C-10 constructed a sixmembered ring. In addition, the HMBC correlations from H-9 to C-8 and C-7 established another six-membered ring. Therefore, compound 2 was assigned as a bicyclic cadinane sesquiterpene [20]. In the ROESY spectrum ( Figure 5), observed cross peaks of H-3/H-5, H-12 and H-5/H-10 indicated that H-3, H-5 and H-10 were in the same orientation, and H-4 was in the other orientation. There, correlations revealed the relative configuration of 2 (3S,4R,5S,6R or 3R,4S,5R,6S). Finally, the absolute configurations were determined by comparing the calculated and experimental ECD spectra (Figure 4). Hence, the structure of 2 was identified and trivially named as albocinnamin B.
Compound 3 was isolated as a yellow solid. Its molecular formula was determined as C 16 H 24 O 3 by HRESIMS (measured at m/z 287.16153 [M + Na] + ; calcd for C 16 H 24 NaO 3 287.16177). The 1 H and 13 C NMR data (Table 1) showed similarities to those of 2, except for the substitutions at C-3 and C-9. There is a hydroxyl group at C-3 of 2, while C-3 of 3 is a methoxy group. Finally, the signal at δ C 76.0 (d, C-9) indicated a OH group placed at C-9. These changes were substantiated by the HMBC correlation from H-16 to C-3, and the 1 H-1 H COSY correlation from H-9 to H-10. In the ROESY spectrum ( Figure 5), observed cross peaks of H-3/H-5, H-12, H-5/H-10 and H-4/H-9 indicated that H-3, H-5 and H-10 were in the same orientation, and that H-4 and H-9 were in the same orientation. Finally, the absolute configuration of 3 was determined by ECD calculations (Figure 4). Consequently, the structure of 3 was identified and trivially named as albocinnamin C. Compound 3 was isolated as a yellow solid. Its molecular formula was determined as C16H24O3 by HRESIMS (measured at m/z 287.16153 [M + Na] + ; calcd for C16H24NaO3 287.16177). The 1 H and 13 C NMR data (Table 1) showed similarities to those of 2, except for the substitutions at C-3 and C-9. There is a hydroxyl group at C-3 of 2, while C-3 of 3 is a methoxy group. Finally, the signal at δC 76.0 (d, C-9) indicated a OH group placed at C-9. These changes were substantiated by the HMBC correlation from H-16 to C-3, and the 1 H-1 H COSY correlation from H-9 to H-10. In the ROESY spectrum ( Figure 5), observed cross peaks of H-3/H-5, H-12, H-5/H-10 and H-4/H-9 indicated that H-3, H-5 and H-10 were in the same orientation, and that H-4 and H-9 were in the same orientation. Finally, the absolute configuration of 3 was determined by ECD calculations (Figure 4). Consequently, the structure of 3 was identified and trivially named as albocinnamin C.
Compound 4 was isolated as a colorless oil. Its molecular formula was determined as C15H22O3 by HRESIMS (measured at m/z 251.16422 [M + H] + ; calcd for C15H23O3 251.16417). Primary analysis of 1D and 2D data (Table 1) was similar to those of 3. The difference was that one carbonyl carbon (δC 204.5) placed at C-3 and one OH group placed at C-8. This conclusion was supported by the HMBC correlations from H-4, H-2 to C-3, and from H-15 to C-6, C-7, and C-8. In the ROESY spectrum, cross peaks of H-5/H-10, H-8, and H-4/H-9 were observed (Figure 2). Considering the homology of biological sources, the absolute configuration of 4 should be the same as 3. Hence, the structure of 4 was identified and trivially named as albocinnamin D.
Compound 5 was isolated as colorless crystals. Its molecular formula was determined as C15H22O3 by HRESIMS (measured at m/z 251.16414 [M + H] + ; calcd for C15H23O3 251.16417), which accounted for five double-bond equivalents. The 1 H NMR and 13 C NMR spectrum ( Table 2) of compound 5 showed signals for 15 carbons, including three CH3, four CH2, three CH, and five non-protonated carbons. Primary analysis of 1D and 2D data showed that 5 was similar to cocumin F [21]. The major difference between 5 and cocumin F is that the oxygenated methylene in 5 replaced the methyl of C-12 in cocumin F, which was confirmed by the HMBC correlations from H-12 to C-9, C-10 and C-11 ( Figure 2). In the ROESY spectrum (  Compound 4 was isolated as a colorless oil. Its molecular formula was determined as C 15 (Table 1) was similar to those of 3. The difference was that one carbonyl carbon (δ C 204.5) placed at C-3 and one OH group placed at C-8. This conclusion was supported by the HMBC correlations from H-4, H-2 to C-3, and from H-15 to C-6, C-7, and C-8. In the ROESY spectrum, cross peaks of H-5/H-10, H-8, and H-4/H-9 were observed ( Figure 2). Considering the homology of biological sources, the absolute configuration of 4 should be the same as 3. Hence, the structure of 4 was identified and trivially named as albocinnamin D.
Compound 5 was isolated as colorless crystals. Its molecular formula was determined as C 15 (Table 2) of compound 5 showed signals for 15 carbons, including three CH 3 , four CH 2 , three CH, and five non-protonated carbons. Primary analysis of 1D and 2D data showed that 5 was similar to cocumin F [21]. The major difference between 5 and cocumin F is that the oxygenated methylene in 5 replaced the methyl of C-12 in cocumin F, which was confirmed by the HMBC correlations from H-12 to C-9, C-10 and C-11 ( Figure 2). In the ROESY spectrum ( Compound 6 was isolated as a colorless oil. Its molecular formula was determined as C 15 (Table 2) showed that it was extremely similar with those of 5, except for the presence of an additional OH group, which was located at C-1, as confirmed by the HMBC correlations from H-8 and H-11 to C-1. In the ROESY spectrum ( Figure 5), observed cross peaks of 1-OH/H-7, H-8, and without cross peaks of H 3 -14/H-7, H-8, indicating that 1-OH, H-7, and H-8 were in the same orientation and H 3 -14 was in the other orientation. Finally, the absolute configuration of 6 was confirmed by ECD calculations (Figure 4). Hence, the structure of 6 was identified and trivially named as albocinnamin F.
Compound 7 was isolated as a colorless oil. Its molecular formula was determined as C 15  249.14852), accounting for six degrees of unsaturation. The 1D data (Table 2) displayed high similarity to those of 5, except for the signals at δ C 143.6 and δ C 135.7, which suggested one double bond between C-1 and C-11 of 7. This assumption was supported by the HMBC correlations from H-8 to C-1, C-11 ( Figure 2). Detailed analysis of 2D NMR data suggested that other parts of 7 were identical to those of 5. The absolute configurations were determined by comparing the calculated and experimental ECD spectra (Figure 4). Therefore, the structure of 7 was established and trivially named as albocinnamin G.
Compound 8 was isolated as a colorless oil. Its molecular formula was determined as C 15 (Table 2) spectra of 8 showed its close resemblance to ochracine F, 15 and the difference of 8 was the presence of one OH group placed at C-9, as supported by the 1 H-1 H COSY correlation from H-9 to H-10 and its molecular weight. In the ROESY spectrum, observed cross peaks of H-9/H-14 indicated H-9 and H-14 in the same orientation ( Figure 5). Considering the homology of biological sources, the absolute configuration of 8 was the same as that of ochracine F. Consequently, the structure of 8 was identified and trivially named as albocinnamin H.
In addition, two known compounds were identified as ochracine F (9) [22] and cerrenin C (10) [23] by comparison of their spectroscopic data to the reported data in the literature. Structurally, compound 1 possessed a new backbone, and it may be derived from a precursor of the cadinane sesquiterpene 2 via a key Baeyer−Villiger oxidation. After further hydrolysis, oxidation, dehydration, and aromatization, a novel product 1 was finally built (Scheme 2).
267.15909). The 1D and 2D NMR data (Table 2) showed that it was extremely similar with those of 5, except for the presence of an additional OH group, which was located at C-1, as confirmed by the HMBC correlations from H-8 and H-11 to C-1. In the ROESY spectrum ( Figure 5), observed cross peaks of 1-OH/H-7, H-8, and without cross peaks of H3-14/H-7, H-8, indicating that 1-OH, H-7, and H-8 were in the same orientation and H3-14 was in the other orientation. Finally, the absolute configuration of 6 was confirmed by ECD calculations ( Figure 4). Hence, the structure of 6 was identified and trivially named as albocinnamin F.
Compound 7 was isolated as a colorless oil. Its molecular formula was determined as C15H20O3 by HRESIMS (measured at m/z 249.14854 [M + H] + ; calcd for C15H21O3 249.14852), accounting for six degrees of unsaturation. The 1D data (Table 2) displayed high similarity to those of 5, except for the signals at δC 143.6 and δC 135.7, which suggested one double bond between C-1 and C-11 of 7. This assumption was supported by the HMBC correlations from H-8 to C-1, C-11 ( Figure 2). Detailed analysis of 2D NMR data suggested that other parts of 7 were identical to those of 5. The absolute configurations were determined by comparing the calculated and experimental ECD spectra (Figure 4). Therefore, the structure of 7 was established and trivially named as albocinnamin G.
Compound 8 was isolated as a colorless oil. Its molecular formula was determined as C15H22O5 by HRESIMS (measured at m/z 305.13573 [M + Na] + ; calcd for C15H22NaO5 305.13594), which accounted for five degrees of unsaturation. Primary analysis of the 1 H and 13 C NMR (Table 2) spectra of 8 showed its close resemblance to ochracine F, 15 and the difference of 8 was the presence of one OH group placed at C-9, as supported by the 1 H-1 H COSY correlation from H-9 to H-10 and its molecular weight. In the ROESY spectrum, observed cross peaks of H-9/H-14 indicated H-9 and H-14 in the same orientation ( Figure  5). Considering the homology of biological sources, the absolute configuration of 8 was the same as that of ochracine F. Consequently, the structure of 8 was identified and trivially named as albocinnamin H.
In addition, two known compounds were identified as ochracine F (9) [22] and cerrenin C (10) [23] by comparison of their spectroscopic data to the reported data in the literature. Structurally, compound 1 possessed a new backbone, and it may be derived from a precursor of the cadinane sesquiterpene 2 via a key Baeyer−Villiger oxidation. After further hydrolysis, oxidation, dehydration, and aromatization, a novel product 1 was finally built (Scheme 2). Previous studies have proved that sesquiterpenes in A. albocinnamomea have cytotoxicity and antibacterial activity [9]. Therefore, all compounds were tested for their cytotoxicity activity against three human cancer cell lines (HL-60, SW480 and MCF-7) and for their antibacterial activity against S. aureus and M. tuberculosis. As a result, compounds 1a Scheme 2. Plausible Biosynthesis Pathway for 1.
Previous studies have proved that sesquiterpenes in A. albocinnamomea have cytotoxicity and antibacterial activity [9]. Therefore, all compounds were tested for their cytotoxicity activity against three human cancer cell lines (HL-60, SW480 and MCF-7) and for their antibacterial activity against S. aureus and M. tuberculosis. As a result, compounds 1a and 1b showed moderate cytotoxicity against SW480 and MCF-7 cells with IC 50 values ranging from 19.3 to 33.3 µM, while compound 2 showed cytotoxicity against HL-60 cells with an IC 50 value of 12.3 µM (Table 3). In addition, compounds 5 and 6 exhibited antibacterial activity against S. aureus with MIC values of 64 and 64 µg/mL, respectively.

Conclusions
A total of ten sesquiterpenes, including eight new ones, have been characterized from the fungus A. albocinnamomea. The new structures with absolute configurations were established by means of spectroscopic methods, single-crystal X-ray diffraction, and ECD calculations. Compounds 1a and 1b showed cytotoxicity against SW480 and MCF-7 cells, while compound 2 displayed cytotoxicity against HL-60 cell. In addition, compounds 5 and 6 exhibited antibacterial activity against S. aureus. This indicates that A. albocinnamomea is rich in sesquiterpenes, which have potential cytotoxicity and antibacterial application prospects.